1. Field of the Invention
The present invention relates to a bumper reinforcement formed of a heat-treatable aluminum alloy extrusion and a method for manufacturing the bumper reinforcement.
2. Description of the Related Art
Japanese Patent Nos. 3465862 and 4111651 and Japanese Unexamined Patent Application Publication Nos. 7-25296 and 2003-118367 disclose the manufacture of automotive reinforcements, such as door beams and bumper reinforcements, that includes crushing an end region of an aluminum alloy extrusion, which is composed of a pair of opposing flanges and a plurality of webs coupled to the flanges, in a direction perpendicular to a surface of the flanges. Japanese Patent No. 4111651 discloses crushing of a press-quenched 6000 series (Al—Mg—Si) aluminum alloy extrusion after age hardening. Japanese Unexamined Patent Application Publication No. 2003-118367 discloses crushing of a press-quenched 6000 or 7000 series (Al—Zn—Mg) aluminum alloy extrusion during T1 tempering after extrusion, and age hardening of the extrusion after the crushing.
Even 7000 series aluminum alloy extrusions after press quenching and before age hardening (T1-tempered members) are hardened through natural aging and suffer a decrease in formability. As described in Japanese Unexamined Patent Application Publication Nos. 7-305151, 10-168553, and 2007-119853, in order to improve formability, 7000 series aluminum alloys hardened through natural aging are subjected to reversion treatment to decrease the strength thereof.
In a bumper reinforcement formed of an aluminum alloy hollow extrusion, crushing of an end portion of the bumper reinforcement as described in Japanese Unexamined Patent Application Publication No. 7-25296 reduces the section modulus of the crushed portion in a horizontal plane. This reduces the reaction force of the bumper reinforcement in a collision of the end portion and thereby reduces the energy absorption of the bumper reinforcement. In the case where the aluminum alloy is a 6000 or 7000 series heat-treatable aluminum alloy, a reversion treatment on the end portion of the bumper reinforcement before the crushing and age hardening after the crushing can prevent cracking caused by crushing and improve the strength of the whole bumper reinforcement. However, this does not essentially solve the problems described above.